Asthma is a complex disease involving the concerted actions of multiple inflammatory and immune cells, spasmogens, inflammatory mediators, cytokines and growth factors. In recent practice there have been four major classes of compounds used in the treatment of asthma, namely bronchodilators (e.g., xcex2-adrenoceptor agonists), anti-inflammatory agents (e.g., corticosteroids), prophylactic anti-allergic agents (e.g., cromolyn sodium) and xanthines (e.g., theophylline) which appear to possess both bronchodilating and anti-inflammatory activity.
Theophylline has been a preferred drug of first choice in the treatment of asthma. Although it has been touted for its direct bronchodilatory action, theophylline""s therapeutic value is now believed to stem also from its anti-inflammatory activity. Its mechanism of action remains unclear. However, it is believed that several of its cellular activities are important in its activity as an anti-asthmatic, including cyclic nucleotide phosphodiesterase inhibition, adenosine receptor antagonism, stimulation of catecholamine release, and its ability to increase the number and activity of suppressor T-lymphocytes. While all of these actually may contribute to its activity, only PDE inhibition may account for both the anti-inflammatory and bronchodilatory components. however, theophylline is known to have a narrow therapeutic index, and a wide range of untoward side effects which are considered problematic.
Of the activities mentioned above, theophylline""s activity in inhibiting cyclic nucleotide phosphodiesterase has received considerable attention recently. Cyclic nucleotide phosphodiesterases (PDEs) have received considerable attention as molecular targets for anti-asthmatic agents. Cyclic 3xe2x80x2,5xe2x80x2-adenosine monophosphate (cAMP) and cyclic 3xe2x80x2,5xe2x80x2-guanosine monophosphate (cGMP) are known second messengers that mediate the functional responses of cells to a multitude of hormones, neurotransmitters and autocoids. At least two therapeutically important effects could result from phosphodiesterase inhibition, and the consequent rise in intracellular adenosine 3xe2x80x2,5xe2x80x2-monophosphate (cAMP) or guanosine 3xe2x80x2,5xe2x80x2-monophosphate (cGMP) in key cells in the pathophysiology of asthma. These are smooth muscle relaxation (resulting in bronchodilation) and anti-inflammatory activity.
It has become known that there are multiple, distinct PDE isoenzymes which differ in their cellular distribution. A variety of inhibitors possessing a marked degree of selectivity for one isoenzyme or the other have been synthesized.
The structure-activity relationships (SAR) of isozyme-selective inhibitors has been discussed in detail, e.g., in the article of Theodore J. Torphy, et al., xe2x80x9cNovel Phosphodiesterase Inhibitors For The Therapy Of Asthmaxe2x80x9d, Drug News and Prospectives, 6(4) May 1993, pages 203-214. The PDE enzymes can be grouped into five families according to their specificity toward hydrolysis of cAMP or cGMP, their sensitivity to regulation by calcium, calmodulin or cGMP, and their selective inhibition by various compounds. PDE I is stimulated by Ca2+/calmodulin. PDE II is cGMP-stimulated, and is found in the heart and adrenals. PDE III is cGMP-inhibited, and inhibition of this enzyme creates positive inotropic activity. PDE IV is CAMP specific, and its inhibition causes airway relaxation, anti-inflammatory and antidepressant activity. PDE V appears to be important in regulating cGMP content in vascular smooth muscle, and therefore PDE V inhibitors may have cardiovascular activity.
While there are compounds derived from numerous structure activity relationship studies which provide PDE III inhibition, the number of structural classes of PDE IV inhibitors is relatively limited. Analogues of rolipram, which has the following structural formula: 
and of Ro-20-1724, which has the following structural formula: 
have been studied.
Rolipram, which was initially studied because of its activity as an antidepressant has been shown to selectively inhibit the PDE IV enzyme and this compound has since become a standard agent in the classification of PDE enzyme subtypes. There appears to be considerable therapeutic potential for PDE IV inhibitors. Besides initial work suggesting an anti-depressive action, rolipram has been investigated for its anti-inflammatory effects, particularly in asthma. In-vitro, rolipram, Ro-20-1724 and other PDE IV inhibitors have been shown to inhibit (1) mediator synthesis/release in mast cells, basophils, monocytes and eosinophils; (2) respiratory burst, chemotaxis and degranulation in neutrophils and eosinophils; and (3) mitogen-dependent growth and differentiation in lymphocytes (The PDE IV Family Of Calcium-Phosphodiesterases Enzymes, John A. Lowe, III, et al., Drugs of the Future 1992, 17(9):799-807).
PDE IV is present in all the major inflammatory cells in asthma including eosinophils, neutrophils, T-lymphocytes, macrophages and endothelial cells. Its inhibition causes down regulation of cellular activation and relaxes smooth muscle cells in the trachea and bronchus. On the other hand, inhibition of PDE III, which is present in myocardium, causes an increase in both the force and rate of cardiac contractility. These are undesirable side effects for an anti-inflammatory agent. Theophylline, a non-selective PDE inhibitor, inhibits both PDE III and PDE IV, resulting in both desirable anti-asthmatic effects and undesirable cardiovascular stimulation. With this well-known distinction between PDE isozymes, the opportunity for concomitant anti-inflammation and bronchodilation without many of the side effects associated with theophylline therapy is apparent. The increased incidence of morbidity and mortality due to asthma in many Western countries over the last decade has focused the clinical emphasis on the inflammatory nature of this disease and the benefit of inhaled steroids. Development of an agent that possesses both bronchodilatory and anti-inflammatory properties would be most advantageous.
It appears that selective PDE IV inhibitors should be more effective with fewer side effects than theophylline.
Attempts have therefore been made to find new compounds having more selective and improved PDE IV inhibition.
It is accordingly a primary object of the present invention to provide new compounds which are effective PDE IV inhibitors.
It is another object of the present invention to provide new compounds which act as effective PDE IV inhibitors with lower PDE III inhibition.
It is a further object of the present invention to provide new compounds which have a substantially equal or superior PDE IV inhibitory effect as compared to theophylline or other known chemical compounds, and which exhibit surprisingly greater selectivity with regard to their PDE inhibitory effects.
It is another object of the present invention to provide a method of treating a patient requiring PDE IV inhibition.
It is another object of the present invention to provide new compounds for treating disease states associated with abnormally high physiological levels of cytokines, including tumor necrosis factor.
It is another object of the present invention to provide a method of synthesizing the new compounds of this invention.
It is another object of the present invention to provide a method for treating a mammal suffering from a disease state selected from the group consisting of asthma, allergies, inflammation, depression, dementia, a disease caused by Human Immunodeficiency Virus and disease states associated with abnormally high physiological levels of cytokines.
With the above and other objects in view, the present invention mainly comprises compounds of the formulae: 
wherein:
Q3, Q6a, Q6b and Q8 are independently a bond, C1-8 alkylene, C2-8 alkenylene and C2-8 alkynylene, and
R3, R6a, R6b and R8 are independently hydrogen, aryl or heteroraryl, optionally substituted by halogen, hydroxy, alkoxy, nitro, cyano and carboxy, provided that:
Q3R3 is not hydrogen or methyl in formulae (I) or (II); and at least one of R3 and R8 is aryl or heteroaryl in formula (I).
The alkylene, alkenylene and alkynylene moieties can be straight or branched, and/or be optionally substituted with an aryl.
When at least one of R3, R6a, R6b, and R8 is aryl, it is preferably phenyl or naphthyl; when at least one of R3, R6a, R6b, and R8 is heteroaryl, it is preferably pyridyl, pyrimidyl, quinolyl or isoquinolyl.
In other aspects of the invention, pharmaceutical compositions and methods of treating mammals suffering from disease states such as asthma, allergies, inflammation, depression, dementia, atopic diseases, rhinitis and the like are provided.
The compounds of the present invention, as demonstrated in the appended examples, are effective in the mediation or inhibition of PDE IV in humans and other mammals. Further, these compounds are selective PDE IV inhibitors which possess both bronchodilatory and anti-inflammatory properties substantially without undesirable cardiovascular stimulation caused by PDE III inhibition. Many of these compounds have a substantially equal or superior PDE IV. inhibitory effect as compared to theophylline.
The present invention is further related to a method for the treatment of allergic and inflammatory disease which comprises administering to a mammal in need thereof an effective amount of the compounds of the present invention.
The present invention is also related to a method for the mediation or inhibition of the enzymatic or catalytic activity of PDE IV activity in mammals, particularly humans, which comprises administering an effective amount of the above-described compounds of the invention to a mammal in need of PDE IV inhibition.
The compounds of the present invention may find use in the treatment of other disease states in humans and other mammals, such as in the treatment of disease states associated with a physiologically detrimental excess of tumor necrosis factor (TNF). TNF activates monocytes, macrophages and T-lymphocytes. This activation has been implicated in the progression of Human Immunodeficiency Virus (HIV) infection and other disease states related to the production of TNF and other cytokines modulated by TNF.
The compounds of the present invention comprise the formulae: 
wherein:
Q3, Q6a, Q6b, and Q8 are independently a bond, C1-8 alkylene, C2-8 alkenylene and C2-8 alkynylene; and
R3, R6a, R6b and R8 are independently hydrogen, aryl or heteroraryl, optionally substituted by halogen, hydroxy, alkoxy, nitro, cyano and carboxy, provided that:
Q3R3 is not hydrogen or methyl in formulae (I) or (II); and at least one of R3 and R8 is aryl or heteroaryl in formula (I).
The C1-8 alkylene, C2-8 alkenylene and C2-8 alkynylene moieties can be straight, branched and/or substituted with an aryl. That is, they can be aralkyl, aralkenyl, or aralkynl groups. Preferable aralkyl moieties include phenalkyl, naphthalkyl and heteroaralkyl.
The alkyl portion of the aralkyl moieties is preferably a lower alkyl. The term xe2x80x9clowerxe2x80x9d is defined for purposes of the present invention as straight or branched chain radicals having from 1 to 3 carbon atoms. When aralkenyl, or aralkynyl embodiments are included, suitable aralkenyl moieties include ethenyl and suitable aralkynyl groups include ethynyl.
The compounds of the present invention are preferably 6-thioxanthines or isoguanine derivatives. One of R3, R6a, R6b, and R8 may be an aryl or a heteroaryl. In this regard, suitable aryl moieties include phenyl and naphthyl. Suitable heteroaryl moieties include pyridyl, pyrimidyl, quinolyl and isoquinolyl.
For example, the compounds of the invention can include phenyl moieties substituted with one or two alkoxy groups, or a halogen, with chlorine being particularly preferred. Some particularly preferred heteroaralkyls include pyridyls.
Although both R3 and R8 can be aryl or aralkyl moieties, in most embodiments, however, at most only one of R3 and R8 is such. Therefore, as an alternative to the aryl and aralkyl moieties set forth above, R3 and R8 can also be hydrogen, such that Q3R3 or Q8R8 can be a C1-9 alkyl which can be branched or unbranched, unsubstituted or substituted with one or more halogens, hydroxy or alkoxy groups, or cycloalkyl groups.
Particularly preferred, however, are hydrogen, methyl, ethyl, propyl, isopropyl and cyclopropyl.
Within the formula set forth above, the following compounds are particularly preferred:
3-(3-cyclopentyloxy-4-methoxybenzyl)-8-isopropyl-6-thio-xanthine;
3-(4-chlorobenzyl)-6-thio-xanthine;
8-isopropyl-3-(4-pyridylmethyl)-6-thio-xanthine;
3-(3-chlorobenzyl)-8-isopropyl-6-thio-xanthine;
3-(4-chlorobenzyl)-N6-ethyl-8-isopropyl-isoguanine;
3-(cyclopropylmethyl)-8-(1-methyl-ethyl)-N6-propyl-isoguanine hydrochloride;
8-cyclopropyl-3, N6-diethyl-isoguanine hydrochloride;
3-(3-cyclopentyloxy-4-methoxybenzyl)-6-thio-xanthine;
3-(4-chlorophenyl)-8-isopropyl-6-thio-xanthine;
8-(3-cyclopentyloxy-4-methoxybenzyl)-3-ethyl-6-thio-xanthine;
8-(3,4-dimethoxybenzyl)-3-propyl-6-thio-xanthine; and
8-(2-naphthylmethyl)-3-propyl-6-thio-xanthine.
Description of the syntheses of these molecules is set forth in the Examples. The syntheses of other molecules not specifically shown in the examples but within the scope of the invention are carried out using those techniques shown with modifications which are known to those of ordinary skill in the art.
The compounds of the present invention have been found to be highly effective PDE IV inhibitors, the inhibition of which is in fact significantly and surprisingly greater than that of theophylline which exhibits 50% inhibition of PDE IV at around 350 xcexcM.
Thus, the concentration which yields 50% inhibition of PDE IV (IC50) for the compound prepared in Example 1 is 1.0 xcexcM, whereas the IC50 for rolipram when run in the same assay was 2.8 xcexcM. It is apparent that this inventive compound is several times as effective as a PDE IV inhibitor as compared to rolipram (or theophylline).
While the IC50 for PDE III inhibition of an Example 1 compound is approximately 25 xcexcM, it is nonetheless clear that it and the other compounds of the invention are highly selective PDE IV inhibitors.
Accordingly, the compounds of the present invention can be administered to anyone requiring PDE IV inhibition. Administration may be orally, topically, by suppository, inhalation or insufflation, or parenterally.
The present invention also encompasses, where appropriate, all pharmaceutically acceptable salts of the foregoing compounds. One skilled in the art will recognize that acid addition salts of the presently claimed compounds may be prepared by reaction of the compounds with the appropriate acid via a variety of known methods. Alternatively, alkali and alkaline earth metal salts are prepared by reaction of the compounds of the invention with the appropriate base via a variety of known methods.
Various oral dosage forms can be used, including such solid forms as tablets, gelcaps, capsules, caplets, granules, lozenges and bulk powders and liquid forms such as emulsions, solution and suspensions. The compounds of the present invention can be administered alone or can be combined with various pharmaceutically acceptable carriers and excipients known to those skilled in the art, including but not limited to diluents, suspending agents, solubilizers, binders, disintegrants, preservatives, coloring agents, lubricants and the like.
When the compounds of the present invention are incorporated into oral tablets, such tablets can be compressed, tablet triturates, enteric-coated, sugar-coated, film-coated, multiply compressed or multiply layered. Liquid oral dosage forms include aqueous and nonaqueous solutions, emulsions, suspensions, and solutions and/or suspensions reconstituted from non-effervescent granules, containing suitable solvents, preservatives, emulsifying agents, suspending agents, diluents, sweeteners, coloring agents, and flavorings agents. When the compounds of the present invention are to be injected parenterally, they may be, e.g., in the form of an isotonic sterile solution. Alternatively, when the compounds of the present invention are to be inhaled, they may be formulated into a dry aerosol or may be formulated into an aqueous or partially aqueous solution.
In addition, when the compounds of the present invention are incorporated into oral dosage forms, it is contemplated that such dosage forms may provide an immediate release of the compound in the gastrointestinal tract, or alternatively may provide a controlled and/or sustained release through the gastrointestinal tract. A wide variety of controlled and/or sustained release formulations are well known to those skilled in the art, and are contemplated for use in connection with the formulations of the present invention. The controlled and/or sustained release may be provided by, e.g., a coating oh the oral dosage form or by incorporating the compound(s) of the invention into a controlled and/or sustained release matrix.
Specific examples of pharmaceutically acceptable carriers and excipients that may be used for formulate oral dosage forms, are described in the Handbook of Pharmaceutical Excipients, American Pharmaceutical Association (1986), incorporated by reference herein. Techniques and compositions for making solid oral dosage forms are described in Pharmaceutical Dosage Forms: Tablets (Lieberman, Lachman and Schwartz, editors) 2nd edition, published by Marcel Dekker, Inc., incorporated by reference herein. Techniques and compositions for making tablets (compressed and molded), capsules (hard and soft gelatin) and pills are also described in Remington""s Pharmaceutical Sciences (Arthur Osol, editor), 1553-1593 (1980), incorporated herein by reference. Techniques and composition for making liquid oral dosage forms are described in Pharmaceutical Dosage Forms: Disperse Systems, (Lieberman, Rieger and Banker, editors) published by Marcel Dekker, Inc., incorporated herein by reference.
When the compounds of the present invention are incorporated for parenteral administration by injection (e.g., continuous infusion or bolus injection), the formulation for parenteral administration may be in the form of suspensions, solutions, emulsions in oily or aqueous vehicles, and such formulations may further comprise pharmaceutically necessary additives such as stabilizing agents, suspending agents, dispersing agents, and the like. The compounds of the invention may also be in the form of a powder for reconstitution as an injectable formulation.
The dose of the compounds of the present invention is dependent upon the affliction to be treated, the severity of the symptoms, the route of administration, the frequency of the dosage interval, the presence of any deleterious side-effects, and the particular compound utilized, among other things.
Various compounds of the present invention are also potent PDE V inhibitors, which reduce smooth muscle cell proliferation and increase pulmonary vasodilation. A combination of of PDE IV and V inhibition is believed to be of benefit in certain medical conditions, such as for inhibition of e.g. restenosis and related diseases.
The PDE IV inhibitory compounds of the present invention may be examined for their PDE IV inhibitory effects via the techniques set forth in the following examples, wherein the ability of the compounds to inhibit PDE IV isolated from bovine tracheal smooth muscle is set forth.